Polishing apparatus that provides a window

ABSTRACT

A polishing pad apparatus includes, a polishing pad, an optically transmissive window framed by an opening through the polishing pad, the window being part of an underlay, and the underlay having a perimeter that extends substantially beyond the perimeter of the window to form a fluid impermeable layer that isolates a rear surface of the window from obstruction by polishing fluid.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of U.S. Provisional PatentApplication Serial No. 60/298,599 filed Jun. 15, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a polishing pad apparatus that providesa window in a polishing pad.

[0004] 2. Related Art

[0005] U.S. Pat. No. 6,045,439 discloses a polishing pad apparatusincluding, a polishing pad mounted on a polishing platen of a polishingmachine. An adhesive, such as, a pressure sensitive adhesive, adheresthe polishing pad to the polishing platen. Successive layers of thepolishing pad, such as, a polishing layer of the polishing pad and oneor more sublayers of the polishing pad, adhere to one another byadditional adhesive. The machine revolves the polishing platen and thepolishing pad, and dispenses a polishing fluid onto the polishing pad.The polishing pad and the polishing fluid polish a semiconductorsubstrate, which removes material from the semiconductor substrate, andwhich provides a smooth, planar polished surface on the semiconductorsubstrate. Further, the polishing pad of the apparatus is adapted with atransparent window. The window is framed by an opening through thepolishing pad. An optical beam is transmitted from an optical detectorapparatus, through a rear of the window, to reflect from the surface ofthe semiconductor substrate. The optical beam monitors the surface ofthe semiconductor substrate, as the substrate is being polished. Theoptical beam is reflected, and transmits through the window fordetection by the optical detector apparatus.

[0006] One of the problems associated with such a polishing padapparatus is, that the polishing fluid seeps behind the polishing pad,and obstructs a rear surface of the window, which contributes toundesired attenuation of the optical beam. Another problem is, that theadhesion strength of the adhesive is reduced when the adhesive becomeswet by leaking polishing fluid, which weakens the adhesion of thepolishing pad to the polishing platen, and which weakens the adhesion ofsuccessive layers of the polishing pad.

[0007] Several sources for fluid seepage exist. The polishing fluid willseep through a polishing pad that is designed to be wetted with thepolishing fluid. Further, the polishing fluid will seep through anunsealed peripheral edge of the polishing pad. Further, the polishingfluid will seep through a leaking seam between the window and theopening. Manufacturing processes have been required to cut and fit thewindow to the opening, and to apply a sealant material in the seam, oralternatively, to mold both the window and the polishing padsimultaneously to join them together at the seam.

[0008] According to WO 01/23141, published PCT applicationPCT/US00/26652, a fluid impermeable layer is provided to span across apolishing layer and a window in an opening through the polishing layer.The fluid impermeable layer is provided with an adhesive forming a bondseal with the polishing layer and a rear surface of the window. The bondseal is a source for fluid seepage. Further, the optical beam transmitsthrough a first interface at the bond layer and the fluid impermeablelayer, and successively through a second interface at the bond layer anda rear surface of the window. Such interfaces tend to attenuate theoptical beam. It would be advantageous to eliminate such interfaces.

[0009] A need exists for a polishing pad apparatus having an opticallytransmissive window framed by an opening through a polishing pad, whichapparatus isolates a rear surface of the window from obstruction bypolishing fluid.

SUMMMARY OF THE INVENTION

[0010] The invention provides a polishing pad apparatus having, apolishing pad, an optically transmissive window framed by an openingthrough the polishing pad, the window being part of an underlay that isunitary with the window, and the underlay having a perimeter thatextends substantially beyond the perimeter of the window to form a fluidimpermeable layer that isolates a rear surface of the window fromobstruction by polishing fluid and from obstruction by the underlay.

[0011] Embodiments of the invention will now be described by way ofexample with reference to the following detailed description taken inconjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a top view of a polishing pad, reduced in size.

[0013]FIG. 1A is an isometric view of a polishing pad in the form of acontinuous belt that is adapted to be mounted on a polishing platen ofbelt configuration.

[0014]FIG. 2 is a fragmentary, enlarged side view of a polishing padapparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, with partsof the apparatus broken away to disclose, a polishing pad having anopening, an underlay having a window, the underlay being adapted formounting on a polishing platen of a polishing machine, and furtherwherein, the underlay is part of the polishing platen, and the polishingpad is removable from the underlay for replacement by another, duplicatepolishing pad

[0015]FIG. 2A is a view similar to FIG. 2, and disclosing a polishingpad apparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, withparts of the apparatus broken away to disclose, a polishing pad having asublayer that is part of the polishing pad, a seal at an edge of thesublayer, and an underlay having a window, the underlay being adaptedfor mounting on a polishing platen of a polishing machine, and furtherwherein, the underlay is a part of the polishing platen, and thesublayer and a remainder of the polishing pad are removable from theunderlay for replacement by another polishing pad.

[0016]FIG. 2B is a fragmentary, enlarged side view of an underlay of apolishing pad apparatus, for example, as disclosed by FIG. 1 or by FIG.1A, adapted for mounting on a polishing platen, with parts of theapparatus broken away to disclose, a window of solid structure.

[0017]FIG. 2C is a view similar to FIG. 2B, and disclosing an underlayof a polishing pad apparatus, for example, as disclosed by FIG. 1 or byFIG. 1A, adapted for mounting on a polishing platen, with parts of theapparatus broken away to disclose, a window substantially coplanar withthe thickness of the underlay.

[0018]FIG. 3 is a fragmentary, enlarged side view of a polishing padapparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, with partsof the apparatus broken away to disclose, a polishing pad, an underlayhaving a window, the underlay being adapted for mounting on a polishingplaten of a polishing machine, and further wherein, the underlay is partof the polishing pad, and the underlay and a remainder of the polishingpad are removable from the polishing platen for replacement by anotherpolishing pad.

[0019]FIG. 3A is a view similar to FIG. 3, and disclosing a polishingpad apparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, withparts of the apparatus broken away to disclose, a polishing pad having asublayer that is part of the polishing pad, a seal at an edge of thesublayer, and an underlay having a window, the underlay being adaptedfor mounting on a polishing platen of a polishing machine, and furtherwherein, the underlay is a part of the polishing pad, and, the underlayand a remainder of the polishing pad are removable from the polishingplaten for replacement by another polishing pad.

[0020]FIG. 3B is a view similar to FIG. 3, and disclosing a polishingpad apparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, withparts of the apparatus broken away to disclose, a polishing pad having asublayer that is part of the polishing pad, and an underlay having awindow, the underlay being adapted for mounting on a polishing platen ofa polishing machine, and further wherein, the underlay is a part of thepolishing pad, and a protruding lip on the underlay provides a seal atan edge of the sublayer.

[0021]FIG. 3C is a view similar to FIG. 3, and disclosing a polishingpad apparatus, for example, as disclosed by FIG. 1 or by FIG. 1A, withparts of the apparatus broken away to disclose an underlay adapted formounting on a polishing platen, and further wherein, the underlay has awindow that is substantially coplanar with the thickness of a remainderof the underlay.

[0022]FIG. 4 is a fragmentary enlarged side view of an underlay having awindow that is fabricated as a hollow structure.

[0023]FIG. 4A is a fragmentary enlarged side view of an underlay havinga window that is fabricated as a solid structure.

[0024]FIG. 4B is a fragmentary enlarged side view of an underlay havinga window, and further disclosing the window as a nonprojecting structurethat is coplanar with the thickness of a remainder of the underlay.

[0025]FIG. 4C is a fragmentary enlarged side view of an underlay havinga window, and further disclosing underlay having a projecting lip thatforms a seal.

DETAILED DESCRIPTION

[0026] Each of FIGS. 1 and 1A, discloses a polishing pad 2 having atleast a top layer 4 for polishing a semiconductor substrate, an opening5 through the top layer 4, and an optically transmissive window 6 framedby the opening 5. The size of the opening 5 is limited, to occupy asmall portion of the top layer 4, which minimizes any difference in theentirety of the polishing activity provided by the polishing layer 4.Each polishing pad 2 has a perimeter 2 a, with the polishing pad 2 ofbelt configuration having a perimeter 2 a along each of the continuousedges of the belt configuration.

[0027] Each of FIGS. 2, 2A, 2B, 2C, 3, 3A, 3B and 3C discloses acorresponding embodiment of a polishing pad apparatus 1 that includes, apolishing pad 2 adapted to be mounted on a polishing platen 3 of a knownpolishing machine. The known polishing machine performs a knownpolishing operation, according to which, the polishing pad 2 is revolvedby the known polishing machine. The polishing pad is accompanied by apolishing fluid to polish a semiconductor substrate that is held by theknown polishing machine. The semiconductor substrate includes, and isnot limited to, for example, a wafer of silicon, a magnetic storagedisk, an optical storage disk, and a semiconductor wafer patterned withconducting circuit interconnects.

[0028] When the polishing pad 2 is revolved, the opening 5 passes overan optical beam of a known optical detector. The window 6 is adapted toalign directly with an opening 3 a through the polishing platen 3. Anoptical beam of the known optical detector transmits through the opening3 a, and through the window 6 to reflect from a surface of asemiconductor substrate being polished by the polishing pad 2.Reflection of the optical beam transmits the optical beam in a reversedirection through the window 6 and through the opening 3 a formonitoring by the known optical detector. Further details are disclosedby U.S. Pat. No. 6,045,439, incorporated by reference herein.

[0029] Further, each corresponding embodiment includes a polishing pad 2having a top layer 4 that projects beyond the window 6. During apolishing operation, the top layer 4 polishes a semiconductor substrate,and is known as a polishing layer of the polishing pad 2. The window 6,being recessed, avoids contact with the semiconductor substrate, as thetop layer 4 contacts the semiconductor substrate during the polishingoperation.

[0030] Prior to the invention, polishing fluid would seep behind the toplayer 4, to obstruct a rear surface 6 a of the window 6, whichcontributed to attenuation of an optical beam. Several sources for fluidseepage continue to exist. The polishing fluid would seep through thetop layer 4, when the top layer 4 is designed to be wetted with thepolishing fluid. Further, the polishing fluid would seep through anunsealed peripheral edge 2 a of the polishing pad 2. When the polishingpad 2 included a sublayer 7, as disclosed by FIGS. 2A, 3A and 3B,beneath the polishing layer 4, fluid would seep through an unsealed edge7 b of the sublayer 7. Prior to the invention, manufacturing processeshave been required to cut and fit the window 6 to the opening 5, and toapply a sealant material in a seam 5 a that is between the window 6 andthe opening 5. Alternatively, manufacturing processes have been requiredto mold both the window 6 and the polishing pad 2 simultaneously to jointhem together at the seam 5 a. However, polishing fluid would seepthrough leaks that would develop in the sealed seam 5 a.

[0031] Each embodiment of the invention provides a polishing padapparatus 1 having an optically transmissive window 6 framed by anopening 5 through a polishing pad 2, which apparatus 1 isolates the rearsurface 6 a of the window 6 from obstruction by polishing fluid. Thewindow 6 is part of an underlay 8. The underlay 8 is unitary with aperimeter 6 b of the window 6. The unitary underlay 8 and window 6eliminate the need for an adhesive bond seal between the underlay 8 andthe window 6, which bond seal would be a source for fluid seepage.Further, because the underlay 8 joins the perimeter 6 b of the window 6,the rear surface of the window 6 is free of an interface with theunderlay 8. Further, the rear surface of the window 6 is without a bondseal between the rear surface of the window and the underlay 6, whichwould contribute to attenuation of an optical beam. The underlay 8 has aperimeter 8 a that extends substantially beyond the perimeter 6 b of thewindow 6 to encompass a large area within its perimeter 8 a. In anembodiment, the perimeter 8 a extends to the perimeter 2 a of the pad 2disclosed by FIG. 1. In another embodiment, the perimeter 8 a extends toat least one perimeter 8 a of the pad 2 of belt configuration disclosedby FIG. 1A. In another embodiment, the perimeter 8 a extends to eachperimeter 8 a of the pad 2 of belt configuration disclosed by FIG. 1A.

[0032] The underlay 8 is fabricated and combined with the polishing padapparatus 1 in a manner to form a fluid impermeable layer that isolatesthe rear surface 6 a of the window 6 from obstruction by polishing fluidthat would otherwise seep behind the polishing pad 2. An adhesive layer10 or an adhesive layer 12 attaches to the underlayer 8. Anotheradhesive layer 9 attaches to a rear surface of the underlayer 8. Eitherone or more than one of the adhesive layers 9, 10 and 12 against theunderlayer 8 provides a corresponding seal extending substantiallybeyond the perimeter 6 b of the window, which isolates the rear surface6 a of the window 6 from obstruction by the polishing fluid. When theunderlay 8 is fabricated from an hydrophobic material, such a materialby itself repels polishing fluid, and isolates the rear surface 6 a ofthe window 6 from obstruction by the polishing fluid.

[0033] Each of FIGS. 2, 2A, 2B and 2C discloses a correspondingembodiment of a polishing pad apparatus 1 wherein, the underlay 8 ispart of the polishing platen 3. The polishing platen 3 is circular formounting the circular polishing pad 2 disclosed by FIG. 1, or thepolishing platen 3 is of belt configuration for mounting the polishingpad 2 of belt configuration disclosed by FIG. 1A. The underlay 8 has anadhesive layer 9 on a rear surface of the underlay 8. The adhesive layer9 has an opening 9 a adapted to be in alignment with an opening 3 athrough the polishing platen 3. For example, the adhesive layer 9 is anadhesive tape with adhesive on opposite sides of the tape.

[0034] As disclosed by FIG. 2, a rear surface of the polishing pad 2 hasan adhesive layer 10 with an opening 10 a adapted to be in alignmentwith the opening 5. A rear surface of the adhesive layer 10 is coveredby a removable covering film 11 that initially adheres to and covers theadhesive layer 10, and is peeled from the adhesive layer 10, as depictedby the arrow, which exposes the adhesive layer 10 for attachmentremovably to the underlay 8.

[0035] The adhesive layer 10 is provided with hollow air transmittingpathways, which pathways allow escape of air that would tend to beentrapped under the adhesive layer 10. The adhesive layer 10, as well asother adhesive layers described herein, have such air transmittingpathways as further disclosed in detail by U.S. patent application Ser.No. 09/660,798 incorporated by reference herein. Each of the otheradhesive layers 9 and 12, is provided with corresponding, hollow airtransmitting pathways.

[0036] When the polishing pad 2 becomes worn out from polishing, the pad2 and the adhesive layer 10 are removable from the underlay 8 forreplacement by another, duplicate polishing pad 2 The underlay 8 remainsas part of the polishing platen 3, and is easily cleaned in preparationfor assembly of a replacement pad 2.

[0037] The underlay 8 itself is removable, together with the adhesivelayer 9, for replacement by a duplicate underlay 8. The polishing pad 2is expected to be replaced more frequently than the underlay 8. Theadhesive layer 10 is advantageously soluble in a solvent that assists inremoval and cleaning of the adhesive layer 10 from the underlay 8. Theadhesive layer 9 is advantageously insoluble in such a solvent, whichpromotes retention of the underlay 8 on the polishing platen 3.

[0038] The embodiment disclosed by FIG. 2A further includes, thepolishing pad 2 having the top layer 4 assembled over and on a sublayer7. The sublayer 7 has an opening 7 a in alignment with the opening 5.Together, the opening 7 a and the opening 5 combine to provide acomposite opening through the polishing pad 2. The adhesive layer 10attaches the top layer 4 to the sublayer 7. A rear surface of thesublayer 7 has an adhesive layer 12 with an opening 12 a in alignmentwith the opening 5. The adhesive layer 12 is covered by the removablecovering film 11 that is peeled from the adhesive layer 12, as depictedby the arrow, which exposes the adhesive layer 12 for attachmentremovably to the underlay 8. The window 6 has a projecting heightsufficient to project into both the opening 7 a the opening 5. A seal 7b is provided at a peripheral edge of the sublayer 7. The seal 7 bincludes, but is not limited to, for example, a heat seal, a pressureembossed seal, and a waterproof coating. The seal 7 b resists seepage ofpolishing fluid into the peripheral edge 7 b that is a part of theperipheral edge 2 a of the polishing pad 2. Further details of the seal7 b are disclosed by U.S. patent application Ser. No. 09/635,877,incorporated herein by reference.

[0039] With reference to the embodiment disclosed by FIG. 2A, when thepolishing pad 2 becomes worn out from polishing, the pad 2 and theadhesive layer 12 are removable from the underlay 8 for replacement byanother, duplicate polishing pad 2. The underlay 8 remains as part ofthe polishing platen 3, and is easily cleaned in preparation forassembly of a replacement pad 2. The underlay 8 itself is removable,together with the adhesive layer 9, for replacement by a duplicateunderlay 8. For this embodiment, the polishing pad 2 is expected to bereplaced more frequently than the underlay 8. The adhesive layer 12 isadvantageously soluble in a solvent that assists in removal and cleaningof the adhesive layer 12 from the underlay 8. The adhesive layer 9 isadvantageously insoluble in such a solvent, which promotes retention ofthe underlay 8 on the polishing platen 3.

[0040] Each of the embodiments disclosed by FIGS. 2 and 2A includes anembodiment of an underlay 8 wherein, the window 6 is a hollow structurethat projects into the opening, as well as being framed by the openingindicated by the numeral 5, or by the composite of numerals 5 and 7 a.FIG. 2B discloses a portion of a polishing pad apparatus 1 having analternative embodiment of the underlay 8 wherein, the window 6 is asolid structure that projects into the opening, as well as being framedby the opening indicated by the numeral 5, or by the composite ofnumerals 5 and 7 a. FIG. 2C discloses a portion of a polishing padapparatus 1 having an alternative embodiment of the underlay 8 wherein,the window 6 has a thickness that is substantially coplanar with athickness of a remainder of the underlay 8, as well as, the window 6being framed by the opening, as indicated by the numeral 5, or asindicated by the composite of numerals 5 and 7 a. The perimeter 6 b ofthe window 6 is indicated by a broken line through the thickness of theunderlay 8.

[0041] Each of FIGS. 3, 3A, 3B and 3C discloses a correspondingembodiment wherein, the underlay 8 is part of the polishing pad 2, suchthat, the underlay 8 and a remainder of the polishing pad 2 areremovable from the polishing platen 3 for replacement by another,duplicate polishing pad 2. The polishing pad 2 has an adhesive layer 10with an opening 10 a adapted to be in alignment with the opening 5. Foreach the embodiments disclosed by FIGS. 3, 3A and 3B, the adhesive layer10 attaches the top layer 4 of the polishing pad 2 to the underlay 8.The rear surface of the underlay has attached thereto an adhesive layer9. The adhesive layer 9 has an opening 9 a adapted to be in alignmentwith both the opening 5 and an opening 3 a through the polishing platen3. For example, the adhesive layer 9 is an adhesive tape with adhesiveon opposite sides of the tape.

[0042] Each of FIGS. 3 and 3C discloses a corresponding embodimentwherein, the adhesive layer 9 is covered by the removable covering film11 that is peeled from the adhesive layer 9, as depicted by the arrow,which exposes the adhesive layer 9 for attachment of the underlay 8 tothe polishing platen 3.

[0043] The embodiment disclosed by FIG. 3 includes the same underlay 8with a window 6 of hollow structure, as disclosed by FIG. 2. Theembodiment disclosed by FIG. 3C includes the same underlay 8 with awindow 6 of substantially the same thickness as a remainder of theunderlay 8, as disclosed by FIG. 2C.

[0044] Each of FIGS. 3A and 3B discloses a corresponding embodimentwherein, the polishing pad 2 has both the top layer 4 and the underlay 8assembled on a sublayer 7. The sublayer 7 has an opening 7 a through itsthickness. The opening 7 a is in alignment with the opening 5. Together,the opening 7 a and the opening 5 combine to provide a composite openingthrough the polishing pad 2. The adhesive layer 9 attaches to thesublayer 7. A rear surface of the sublayer 7 has an adhesive layer 12with an opening 12 a adapted to be in alignment with the opening 5. Theadhesive layer 12 is covered by the removable covering film 11 that ispeeled from the adhesive layer 12, as depicted by the arrow, whichexposes the adhesive layer 12 for attachment removably to the underlay8. A seal 7 b is provided at a peripheral edge of the sublayer 7. Forthis embodiment, the seal 7 b is a unitary projecting lip on theperimeter 8 a on the underlay 8. The lip extends at and over theperipheral edge of the sublayer 7. The window 6 has a projecting heightsufficient to project into both the opening 7 a and the opening 5.

[0045] The embodiment disclosed by FIG. 3A includes an underlay 8 havinga window 6 of hollow structure, similar to that disclosed by FIG. 2. Theembodiment disclosed by FIG. 3B includes an underlay 8 having a window 6of solid structure the same as in the embodiment disclosed by FIG. 2B.

[0046] Each of FIGS. 4, 4A, 4B and 4C discloses a correspondingembodiment of the underlay 8 and the window 6 fabricated as a unitarystructure. For example, the underlay 8 and the window 6 are fabricatedby shaping a fluent material, and solidifying the fluent material to asolid phase that is optically transparent. The fluent material is shapedin a cavity 13 defined between two, opposed shaping dies 14, 14 a of aknown molding apparatus, or alternatively, a known sintering apparatus.The dies 14, 14 a meet along a parting line 14 b. The dies 14, 14 afabricate the fluent material into the underlay 8 as a thin layer.Further, the dies 14, 14 a fabricate the window 6 in a window shapedrecess 14 c defined between the dies 14, 14 a. Alternatively, asdisclosed by FIG. 4, the window 6 is vacuum formed, by drawing a reducedatmosphere through an exhaust vent 14 d provided in the shaping die 14to communicate with the window shaped recess 14 c. Followingsolidification of the fluent material between the dies 14, 14 a, thedies 14, 14 a are opened along the parting line 14 b, which allowsremoval of the underlay 8 and unitary window 6. Alternatively, thefluent material is a melt that is shaped and solidified between the dies14, 14 a that are molding dies of a known molding apparatus.Alternatively, the fluent material is a powder mixed with a sinteringbinder that is shaped between the dies 14, 14 a serving as sinteringpreforms. During a known heat sintering operation the powder binds toitself, and the binder is driven off by heat. The fluent material issolidified as a sintered material that is optically transparent in thesolid phase.

[0047]FIG. 4 discloses an embodiment of the underlay 8 having the window6 fabricated as a thin and hollow structure. The recess 14 c is narrowlyspaced from the opposed die 14 a, which defines a relatively thin spacein the cavity 13 within which the dies 14, 14 a fabricate the hollowwindow 6.

[0048]FIG. 4A discloses an embodiment of the underlay 8 having thewindow 6 fabricated as a thick and solid structure. The recess 14 c issubstantially spaced from the opposed die 14 a, defining a relativelywide space in the cavity 13 within which the dies 14, 14 a fabricate thesolid window 6 from the solidified fluent material.

[0049]FIG. 4B discloses an embodiment of the underlay 8 having thewindow 6 as a nonprojecting structure. The cavity 13 is spaced from theopposed die 14 a the same distance as is a remainder of the cavity 13within which the dies 14, 14 a fabricate the window 6 from thesolidified fluent material. The dies 14, 14 a fabricate the window 6with a thickness that is substantially coplanar with the remainder ofthe underlay 8.

[0050]FIG. 4C discloses an embodiment of the underlay 8 having aprojecting lip 7 b, according to FIG. 3A The following materials aresuitable for being transmissive of the optical beam of the known opticaldetector; PET, polyethyleneterapthalate, PE, polyethylene, PP,polypropylene, PU, polyurethane and PVC, polyvinylchloride, could beused in varying thickness of thin sheets.

[0051] The invention further attains a reduced cost of production byeliminating the need for die cutting the shape of the window to interfitwith the opening in the pad. The invention eliminates the disadvantageof a leaking seal between the window and the opening through thepolishing layer 4 of the polishing pad 2.

What is claimed is:
 1. A polishing pad apparatus comprising: a polishingpad for polishing a semiconductor substrate with a polishing fluid, anoptically transmissive window framed by an opening through the polishingpad, the window being part of an underlay that is unitary with thewindow, and the underlay having a perimeter that extends substantiallybeyond the perimeter of the window to form a fluid impermeable layerthat isolates a rear surface of the window from obstruction by polishingfluid and from obstruction by the underlay.
 2. A polishing pad apparatusas recited in claim 1 wherein, the underlay is fabricated from ahydrophobic material.
 3. A polishing pad apparatus as recited in claim 1wherein, the window projects outwardly of a remainder of the underlayand within the opening.
 4. A polishing pad apparatus as recited in claim1 wherein, the window projects within the opening, and a seam betweenthe window and the opening is sealed.
 5. A polishing pad apparatus asrecited in claim 1 wherein, the window projects within the opening, anda seam between the window and the opening is unsealed.
 6. A polishingpad apparatus as recited in claim 1, and further comprising: theunderlay having a first contact adhesive that attaches the underlay to apolishing platen of a polishing machine, and the polishing pad having asecond contact adhesive that removably attaches the polishing pad to theunderlay.
 7. A polishing pad apparatus as recited in claim 1, andfurther comprising: the underlay having a first contact adhesive thatremovably attaches the underlay to a polishing platen of a polishingmachine, and the polishing pad having a second contact adhesive thatpermanently attaches the polishing pad to the underlay.
 8. A polishingpad apparatus as recited in claim 1 wherein, the underlay is part of thepolishing platen, and the polishing pad is removable from the underlayfor replacement by another polishing pad.
 9. A polishing pad apparatusas recited in claim 1 wherein, the underlay is part of the polishingpad, and the underlay and a remainder of the polishing pad removablefrom the polishing platen for replacement by another polishing pad. 10.A polishing pad apparatus as recited in claim 1, and further comprising:the polishing pad having a sublayer that is part of the polishing pad, aseal at an edge of the sublayer, and further wherein, the underlay is apart of the polishing platen, and the sublayer and a remainder of thepolishing pad are removable from the underlay for replacement by anotherpolishing pad.
 11. A polishing pad apparatus as recited in claim 1, andfurther comprising: the polishing pad having a sublayer that is part ofthe polishing pad, a seal at an edge of the sublayer, and furtherwherein, the underlay is a part of the polishing pad, and the underlayand a remainder of the polishing pad are removable from the polishingplaten for replacement by another polishing pad.
 12. A polishing padapparatus as recited in claim 1, and further comprising: the polishingpad having a sublayer that is part of the polishing pad, a seal at anedge of the sublayer, the underlay having a projecting lip that formsthe seal at the edge of the sublayer, and further wherein, the underlayis a part of the polishing pad, and the underlay and a remainder of thepolishing pad are removable from the polishing platen for replacement byanother polishing pad.
 13. A polishing pad apparatus, comprising: apolishing pad having at least a top layer for polishing a semiconductorsubstrate with a polishing fluid, an opening through the top layer, andan optically transmissive window framed by the opening, and furtherwherein, the window is part of an underlay that is unitary with thewindow, and the underlay extends substantially from the window andsubstantially beyond the perimeter of the window to form anuninterrupted and continuous, fluid impermeable layer that isolates arear surface of the window from obstruction by the underlay and fromobstruction by the polishing fluid.
 14. A polishing pad apparatus asrecited in claim 13 wherein, the underlay is fabricated from ahydrophobic material.
 15. A polishing pad apparatus as recited in claim13 wherein, the window projects outwardly of a remainder of the underlayand within the opening.
 16. A polishing pad apparatus as recited inclaim 13 wherein, the window projects within the opening, and a seambetween the window and the opening is sealed.
 17. A polishing padapparatus as recited in claim 13 wherein, the window projects within theopening, and a seam between the window and the opening is unsealed. 18.A polishing pad apparatus as recited in claim 13, and furthercomprising: the underlay having a first contact adhesive that attachesthe underlay to a polishing platen of a polishing machine, and thepolishing pad having a second contact adhesive that removably attachesthe polishing pad to the underlay.
 19. A polishing pad apparatus asrecited in claim 13, and further comprising: the underlay having a firstcontact adhesive that removably attaches the underlay to a polishingplaten of a polishing machine, and the polishing pad having a secondcontact adhesive that permanently attaches the polishing pad to theunderlay.
 20. A polishing pad apparatus as recited in claim 13 wherein,the underlay is part of the polishing platen, and the polishing pad isremovable from the underlay for replacement by another polishing pad.21. A polishing pad apparatus as recited in claim 13 wherein, theunderlay is part of the polishing pad, and the underlay and a remainderof the polishing pad are removable from the polishing platen forreplacement by another polishing pad.
 22. A polishing pad apparatus asrecited in claim 13, and further comprising: the polishing pad having asublayer that is part of the polishing pad, a seal at an edge of thesublayer, and further wherein, the underlay is a part of the polishingplaten, and the sublayer and a remainder of the polishing pad areremovable from the underlay for replacement by another polishing pad.23. A polishing pad apparatus as recited in claim 13, and furthercomprising: the polishing pad having a sublayer that is part of thepolishing pad, a seal at an edge of the sublayer, and further wherein,the underlay is a part of polishing pad, and the underlay and aremainder of the polishing pad are removable from the polishing platenfor replacement by another polishing pad.
 24. A polishing pad apparatusas recited in claim 13, and further comprising: the polishing pad havinga sublayer that is part of the polishing pad, a seal at an edge of thesublayer, the underlay having a projecting lip that forms the seal atthe edge of the sublayer, and further wherein, the underlay is a part ofthe polishing pad, and the underlay and a remainder of the polishing padare removable from the polishing platen for replacement by anotherpolishing pad.
 25. A polishing pad apparatus, comprising: a polishingpad having at least a top layer for polishing a semiconductor substratewith a polishing fluid, an opening through the top layer, and anoptically transmissive window framed by the opening, and furtherwherein, the window is part of an underlay, a perimeter of the underlayextends substantially beyond a perimeter of the window to form a fluidimpermeable layer that isolates a rear surface of the window fromobstruction by the polishing fluid.
 26. A polishing pad apparatus asrecited in claim 25 wherein, the underlay is fabricated from ahydrophobic material.
 27. A polishing pad apparatus as recited in claim25 wherein, the window projects outwardly of a remainder of the underlayand within the opening.
 28. A polishing pad apparatus as recited inclaim 25 wherein, the window projects within the opening, and a seambetween the window and the opening is sealed.
 29. A polishing padapparatus as recited in claim 25 wherein, the window projects within theopening, and a seam between the window and the opening is unsealed. 30.A polishing pad apparatus as recited in claim 25, and furthercomprising: the underlay having a first contact adhesive that attachesthe underlay to a polishing platen of a polishing machine, and thepolishing pad having a second contact adhesive that removably attachesthe polishing pad to the underlay.
 31. A polishing pad apparatus asrecited in claim 25, and further comprising: the underlay having a firstcontact adhesive that removably attaches underlay to a polishing platenof a polishing machine, and the polishing pad having a second contactadhesive that permanently attaches the polishing pad to the underlay.32. A polishing pad apparatus as recited in claim 25 wherein, theunderlay is part of the polishing platen, and the polishing pad isremovable from the underlay for replacement by another polishing pad.33. A polishing pad apparatus as recited in claim 25 wherein, theunderlay is part of the polishing pad, and the underlay and a remainderof the polishing pad are removable from the polishing platen forreplacement by another polishing pad.
 34. A polishing pad apparatus asrecited in claim 25, and further comprising: the polishing pad having asublayer that is part of the polishing pad, a seal at an edge of thesublayer, and further wherein, the underlay is a part of the polishingplaten, and the sublayer and a remainder of the polishing pad areremovable from the underlay for replacement by another polishing pad.35. A polishing pad apparatus as recited in claim 25, and furthercomprising: the polishing pad having a sublayer, and further wherein,the underlay has a projecting lip providing a seal at the edge of thesublayer.
 36. A polishing pad apparatus as recited in claim 25, andfurther comprising: the polishing pad having a sublayer that is part ofthe polishing pad, a seal at an edge of the sublayer, and furtherwherein, the underlay is a part of the polishing pad, and the underlayand a remainder of the polishing pad are removable from the polishingplaten for replacement by another polishing pad.
 37. A polishing padapparatus as recited in claim 25, and further comprising: the polishingpad having a sublayer that is part of the polishing pad, a seal at anedge of the sublayer, the underlay having a projecting lip that formsthe seal at the edge of the sublayer, and further wherein, the underlayis a part of the polishing pad, and the underlay and a remainder of thepolishing pad are removable from the polishing platen for replacement byanother polishing pad.
 38. A polishing pad apparatus, comprising: apolishing pad having at least a top layer for polishing a semiconductorsubstrate with a polishing fluid, an opening through the top layer, andan optically transmissive window framed by opening, and further wherein,the window is part of an underlay that is unitary with the window, theunderlay having an adhesive thereon, and a perimeter of the underlayhaving the adhesive thereon extends substantially beyond a perimeter ofthe window to form an uninterrupted and continuous, fluid impermeablelayer that isolates a rear surface of the window from obstruction by thepolishing fluid.
 39. A polishing pad apparatus as recited in claim 38wherein, the underlay is fabricated from a hydrophobic material.
 40. Apolishing pad apparatus as recited in claim 38 wherein, the windowprojects outwardly of a remainder of the underlay and within theopening.
 41. A polishing pad apparatus as recited in claim 38 wherein,the window projects within the opening, and a seam between the windowand the opening is sealed.
 42. A polishing pad apparatus as recited inclaim 38 wherein, the window projects within the opening, and a seambetween the window and the opening is unsealed.
 43. A polishing padapparatus as recited in claim 38, and further comprising: the underlayhaving a first contact adhesive that attaches the underlay to apolishing platen of a polishing machine, and the polishing pad having asecond contact adhesive that removably attaches the polishing pad to theunderlay.
 44. A polishing pad apparatus as recited in claim 38, andfurther comprising: the underlay having a first contact adhesive thatremovably attaches the underlay to a polishing platen of a polishingmachine, and the polishing pad having a second contact adhesive thatpermanently attaches the polishing pad to the underlay.
 45. A polishingpad apparatus as recited in claim 38 wherein, the underlay is part ofthe polishing platen, and the polishing pad is removable from theunderlay for replacement by another polishing pad.
 46. A polishing padapparatus as recited in claim 38 wherein, the underlay is part of thepolishing pad, and the underlay and a remainder of the polishing areremovable from the polishing platen for replacement by another polishingpad.
 47. A polishing pad apparatus as recited in claim 38, and furthercomprising: the polishing pad having a sublayer that is part of thepolishing pad, a seal at an edge of the sublayer, and further wherein,the underlay is a part of the polishing platen, and the sublayer and aremainder of the polishing pad are removable from the underlay forreplacement by another polishing pad.
 48. A polishing pad apparatus asrecited in claim 38, and further comprising: the polishing pad having asublayer that is part of the polishing pad, a seal at an edge of thesublayer, and further wherein, the underlay is a part of the polishingpad, and the underlay and a remainder of the polishing pad are removablefrom the polishing platen for replacement by another polishing pad. 49.A polishing pad apparatus as recited in claim 38, and furthercomprising: the polishing pad having a sublayer that is part of thepolishing pad, a seal at an edge of the sublayer, the underlay having aprojecting lip that forms the seal at the edge of the sublayer, andfurther wherein, the underlay is a part of the polishing pad, and theunderlay and a remainder of the polishing pad are removable from thepolishing platen for replacement by another polishing pad.
 50. Apolishing pad apparatus as recited in claim 38, and further comprising:the polishing pad having a sublayer, and further wherein, the underlayhas a projecting lip providing a seal at the edge of the sublayer.